It has become desirable to measure the amount of fuel that has contaminated or diluted oil, usually motor oil. In one example, diesel engine technology has advanced significantly over the last decade. Modern diesel engines utilize advanced injector technology to enable multiple injections of fuel per combustion cycle. Precise control of injection timing allows optimization of engine efficiency, engine out emissions, and engine noise, vibration, and harshness. Furthermore, engines are being operated under specific modes to enable after treatment devices in the exhaust system to control pollutants.
One application where the control of fuel injection offers a great advantage is the operation of the diesel engine in net-fuel-rich modes to regenerate lean NOx trap catalysts. The regeneration is necessary for catalyst operation which reduces engine out NOx to regulated levels. During engine operation for catalyst regeneration, extra fuel is injected into the cylinder often in conjunction with throttling or higher exhaust gas recirculation rates to generate rich exhaust. The reductants present in the rich exhaust regenerate the catalyst, and specific parameters of the engine rich mode are adjusted to control both the overall magnitude and chemistry of the exhaust reductant mixture. However, extra fuel injection into the cylinder can lead to other issues of concern such as torque control, noise and vibration control, and oil dilution. In some cases oil dilution by diesel fuel can occur at levels that may impact engine durability.
A challenge for diesel automotive engineers is to establish lean NOx trap regeneration strategies that optimally regenerate the lean NOx trap without creating undesirable secondary emissions (e.g., soot or unburned HCs) in the tailpipe and without causing significant fuel dilution of the engine oil. Fuel impingement of the cylinder wall oil film becomes more likely as the extra fuel injection timing is further delayed from top dead center. Injection timing also affects the reductant chemistry produced. Thus, optimization of the lean NOx trap reductant chemistry and minimization of fuel dilution are linked; both are affected by enrichment parameters. Measurement and feedback on the dilution of oil by fuel during the process is valuable in efficiently determining the optimal conditions to operate the engine.
Although an example has been set forth above to show need and utility of the invention, there are various and sundry other circumstances in which it is desirable to measure at least one of the amount, concentration, and addition (or leakage) rate of fuel that has contaminated or diluted oil, usually, but not always, motor oil.